Move signal handling to libuv event loop

This removes all signal handling code from os_unix.c to os/signal.c. Now signal
handling is done like this:

- Watchers for signals are registered with libuv default event loop
- `event_poll` continuously calls `poll_uv_loop` to produce events until it
  receives user input, SIGINT or a timeout
- Any signals received in `poll_uv_loop` will push events to a queue that is
  drained and processed by `event_poll`

Signals aren't handled directly in the libuv callback to avoid recursion in the
event loop(which isn't supported by libuv).

The same principle will apply to other events in the future: Push to a queue
from a libuv callback and drain it from `event_poll`

1 files changed, 13 insertions, 0 deletions

diff --git a/src/os/signal.h b/src/os/signal.h
new file mode 100644
index 0000000000..a5247742db
--- /dev/null
+++ b/src/os/signal.h
@@ -0,0 +1,13 @@
+#ifndef NEOVIM_OS_SIGNAL_H
+#define NEOVIM_OS_SIGNAL_H
+
+#include "os/event.h"
+
+void signal_init(void);
+void signal_stop(void);
+void signal_accept_deadly(void);
+void signal_reject_deadly(void);
+void signal_handle(Event *event);
+
+#endif
+